Evaluate object rules (group assign) before and after creating objects with apply rules.

Refs #6105
Add AddGroup() for host, service, user objects.

Refs #6105
Group assign requires object.groups update too (for apply rules).

Refs #6105
Allow EvaluateRules() to keep rules for the next iteration.

Refs #6105
Make AddGroup() unique.

Refs #6105
Merge branch 'fix/apply-req-group-assign-6105' into next

Fixes #6105